A variety of relatively “hard” fat compositions, e.g., margarine, spreads, shortening, and frying fat, are formed from seed oils and vegetable oils. For example, plastic fat compositions such as margarine and low-fat spreads typically comprise an emulsion of an oil phase (typically including a liquid oil and a hard fat, which usually has been hardened) with an aqueous phase, together with various emulsifiers, stabilizers, preservatives, and flavoring agents.
Most seed oils and vegetable oils, such as soybean oil, rapeseed oil, corn oil, sunflower oil, palm oil, or linseed oil, contain a variety of saturated and unsaturated fatty acids. The fatty acid profiles of oils commonly vary by source, but typically include a variety of saturated fatty acids, such as palmitic acid (C16:0) and stearic acid (C18:0); some monounsaturated fatty acids such as oleic acid (C18:1) and erucic acid (C22:1); and polyunsaturated fatty acids including linoleic acid (C18:2) and linolenic acid (C18:3). (The Cx:y designation refers to fatty acids wherein x is the number of carbon atoms and y is the number of double bonds.)
Polyunsaturated fatty acids, particularly linolenic acid (C18:3), are known to oxidize over time with oxidation proceeding more quickly at higher temperatures such as those used in baking, frying, etc. This oxidation leads to unacceptable rancid flavors. Hence, high contents of linolenic acid can also render edible fats unstable and easily oxidized during cooking and storage, which compromises the sensory characteristics of foods cooked in or incorporating such fats. Many edible fats are hydrogenated to increase stability by reducing the amount of linolenic acid and increasing saturated and monounsaturated fatty acids. For example, the maximum desirable linolenic acid content for many commercial bakery and frying shortenings is about two weight percent of the total fatty acid content of the fat.
Hydrogenating (mono)unsaturated fatty acids increases the saturated fatty acid content. Unduly high saturated fatty acid content in one's diet can adversely impact cardiovascular health by raising serum cholesterol levels. As a byproduct of hydrogenation, unsaturated fatty acids can, be converted from their natural cis configuration to their trans isomer form. Recent studies have indicated that trans-fatty acids may impact cardiovascular health more negatively than saturated fatty acids do. In part due to this recent research, consumers are becoming attentive to the trans-fatty acid content of their diets and many consumers are beginning to prefer products with lower trans-fatty acid content.